The Destiny Trap
by redstarsarc
Summary: The Fourth and Tenth Doctors switch bodies. And there's something lurking in the TARDIS, something no one can quite remember...


**A/N: Here it is, a story featuring both Four AND Ten! This spawned from my bored, heat-addled mind one evening when I decided I really didn't want to write about space pirates. So yeah, when I procrastinate with my real stories, I write random fanfiction instead :). So anyway, I hope you all enjoy.**

* * *

 **The Destiny Trap**

 _Earth, 2007 A.D._

He watched her burn. Amid the fire and rain, she writhed and screamed, the once fierce Empress of the Racnoss now consumed by fear and grief for her children. It was mesmerizing. It was horrible.

The Doctor had seen so much, had saved worlds – this one in particular – countless times. Each victim killed made his hearts cry out in guilt and regret. But each enemy whose death he'd caused – needed – chipped away at his very soul. He felt the weight of that burden as he vanquished yet another enemy.

The Earth was saved once again and at great cost, as these sort of victories usually were, but the Doctor was always willing to pay it.

From the balcony, Donna called out to him.

He didn't hear her.

* * *

 _Skaro, 1500 A.D._

This was it. All those senseless deaths, all the suffering…it could end. Right here, right now. What was more, he could prevent any of that from ever happening, wipe it clean from the timeline.

All it took was a single detonation. No more Daleks. But even with the two wires in his hands, his enemies' deaths literally at his fingertips, he hesitated.

"Have I the right?" he wondered. Thousands, maybe even millions, of lives on his hands. No one should ever have this much power. And yet…and yet…

He'd seen what they'd done or rather what they would do. They were pure killing machines. With all sympathy and compassion removed, they had been engineered for war. He wasn't so much killing them as he was saving the countless lives they would go on to destroy.

He brought the two wires together.

* * *

 _Somewhere in another dimension_

Lights flickered and dimmed inside the TARDIS. Within the console, the heart flared, reacting to a disturbance in the time stream and mirroring the unease of a younger TARDIS farther back along the time stream.

Hesitantly, the cloister bell began to ring.

* * *

 _The TARDIS, Earth, 2007 A.D._

The Doctor jolted upright and wondered what he was doing lying on the floor of the TARDIS. A TARDIS that looked disturbingly different than when he'd last seen it. And the cloister bell was ringing. That wasn't good.

"Sarah!" he called out. "Harry!"

No answer.

To add to the growing pile of mysteries, he felt strange. For a start, his voice sounded different and his teeth were smaller. When he tried to stand, he tripped over unfamiliar legs.

"I'm taller than I remember," he said dumbly. "I…" He tried again, pulling himself up beside the console and putting a hand on his head. His eyes widened. _Hair!_ he thought. _What happened to –_

"No," he gasped. "No, it can't be." But the proof was right here, in his voice and in his teeth, legs, hands, hair. "I've regenerated." He breathed slowly, felt the contours of his unfamiliar face with one hand. "I've regenerated and I slept through the whole thing." _But what…how could…?_

"No, wait," he said, trying to still his racing thoughts. "Brain. I still have my own brain, that hasn't changed." This was wrong, all wrong. He found a small mirror hanging off one of the odd branch-like things and studied himself in it. He touched his nose, felt the tips of his ears, put a hand to his chest – still had two hearts, at least.

"But why don't I remember?" He'd been about to destroy the Daleks, he'd looked up and then…

The lights in the TARDIS dimmed. He was alone here, that much he'd figured. Except…somehow it didn't feel so lonely as alone should be.

* * *

 _The TARDIS, lost in transit_

The Doctor ran for the console, flipped switches, glanced at the data screen. The center column moved with a low thrum and the screen showed him endless strings of numbers, continually changing temporal-spatial coordinates as they passed through the Time Vortex. The only problem was that he hadn't done anything. Something was controlling the TARDIS but it certainly wasn't him.

"Doctor, what is it? What's wrong?"

He spun around and his face split into a wide grin. "Sarah Jane Smith, it's been too long," he said. "And Harry!"

"You saw us a few minutes ago," Harry said uncertainly.

"Right. Yeah." He went back to the controls, turned on the internal scanner. As he did, the lights flickered. "I don't want to start a panic, but we're not alone."

"What do you mean?" Sarah asked.

"There's something hiding in the TARDIS."

A sense of unease fell over the console room. The sound of distant groaning – energy coursing through the pipes – provided an eerie backdrop to the proclamation.

"Doctor…" Harry was peering at the small screen that hung over the console. "How did you know to do an internal scan?"

"'Cause this has happened before. Well, it will happen. Er, well I remember it in the future when I became who I am now except now I'm who I was then so I don't know _exactly_ how it'll pan out the second time around. Er, the first." He stopped, watching the confused looks on his companions' faces. Without thinking, he went to run his fingers through his hair but stopped when he felt the mop of brown curls on his head. It was still weird, reliving a moment nearly five-hundred years into his past.

"Problem is," the Doctor continued, "I can't actually remember what it is that's in the TARDIS in the first place."

Sarah Jane and Harry exchanged a look, thinking perhaps the Doctor had finally snapped.

* * *

 _The TARDIS, Earth, 2007 A.D._

"Where is it, where is it?" The Doctor dug through piles of discarded garments, gizmos, and knick-knacks haphazardly shoved into a closet in one of the side rooms. Really, since when had he become so messy?

"Aha!" he exclaimed as he spotted what he was looking for under an old recorder and a rather garish patchwork coat. Smiling to himself, he draped the overly long scarf about his shoulders and sat down on the pile, feeling comfortable with the familiarity.

He stayed there for several minutes, trying to get his thoughts in order. Definitely not a regeneration, of that he was sure. The only thing that made sense was that he'd been subject to temporal psychological transference. He slowly got to his feet. He would need to set the TARDIS' scanners to do a sweep for temporal energy. Whatever was responsible, be it sentient being or natural phenomenon, he needed to find it.

The lights in the room flickered. The Doctor felt just the briefest disorientation, a sense of getting up too fast, something swimming in his vision, and then it was gone just as swiftly as it had come.

Shaking his head, he was about to return to the console room when something caught his eye and he froze. There were words on the wall, words he knew hadn't been there before. They were written in pen, hastily scrawled and at an angle as if the writer hadn't been looking at the words as he wrote them. But there was something familiar about the handwriting, though he didn't know what. The words simply said, 'turn around.'

Slowly, the Doctor turned.

* * *

 _The TARDIS, lost in transit_

The Doctor ran down the corridor with a length of coiled wire under his arm, the coil leaving a trail behind him on the floor and all the way to the console room.

"Doctor, what are you doing?" Sarah yelled at him, chasing him down the corridor while Harry, as asked, remained in the console room.

"No idea!" he answered without breaking stride. Still, he periodically checked the palm of his left hand where there was written 'cord/0r.' Still nothing new. A sense of unease rose within him – he still didn't know how the phrase had gotten there – but something in his gut told him to trust it.

"Doctor!" Sarah gasped and the shock in her voice stopped the Doctor in his tracks. "What is that thing?" She was looking into one of the side rooms, its door left open. Her face was pale.

"Sarah." The Doctor reached out a hand to touch her shoulder and she flinched, turning sharply to look at him. He barely registered the change in her expression as he peered into the room but there was nothing there. "What was it? What did you see?"

"What was what?" Sarah said.

The Doctor looked back at her and realized the shock and fear were gone, replaced by confusion.

"The thing in the room you said you saw," the Doctor said.

She frowned. "I didn't see anything."

The Doctor furrowed his brow. He glanced again at the writing on his hand. Still nothing new but suddenly its appearance was beginning to make a terrifying sort of sense.

* * *

 _The TARDIS, Earth, 2007 A.D._

The Doctor was running deeper into the TARDIS, scarf wrapped several times around his shoulders. Everywhere he looked upon the walls were numbers. Counting up. Five…six…seven. He didn't slow, didn't dare look behind him. Ten…eleven…twelve.

He rounded a corner and found himself in the Oxygen Room. Thick oak trees towered over him and grass coated the floor, lush and green. The air was alive with the calls of birds and the buzzing of bees. Small flowers blossomed here and there, growing in pink clusters among the blades of grass. High above the canopy of the trees was a series of thick hollow tubes constantly at work sucking up the oxygen and distributing it throughout the TARDIS using the ventilation system. He'd been meaning to replace the broken down air filtration system for some time but never had and this room seemed like a nice alternative.

He made his way through the trees, branches tugging at his hair and clothes. It was warm in here. He shrugged out of the long brown coat but refused to take off the scarf.

Somewhere nearby, he could hear the steady drip…drip…drip of water over rock. Puzzled, he followed the sound until he found its source: a small rocky cliff that had once had a waterfall that cascaded to a forest stream below. Now the stream was dry and only the smallest trickle of water dripped onto the rocks below.

Reaching beneath a tuft of vegetation growing from the rock, he grasped a small knob and turned it, squeaking in protest, until the trickle died away. Then he listened in the sudden silence. Even the songbirds and the bees had ceased their music.

And on the stone, where there hadn't been before, was a number.

Fifty-nine.

* * *

 _The TARDIS, lost in transit_

When finally the Doctor reached the Zero Room, he stopped, glanced again at his palm and, seeing nothing, he entered the room.

Suddenly everything was quiet. Not only was the drone of the engine gone and the sounds of the metal in the hallway, the energy conduits, the breathing of this vast ship, but so too was his mind, suddenly cut off from the usual psychic cacophony the universe bombarded him with. This was a place for rest and recuperation, a place where he could think.

"Doctor?" Sarah Jane said as she came into the room. Her voice was quiet, oddly muffled. She stopped just inside the door. "Whoa. What is this place?"

"Zero Room," the Doctor answered absentmindedly. He felt along the white wall between large roundels like the ones in the console room, occasionally pressing his ear to it. After trying this several times, he finally nodded to himself, backed away, and took out the sonic screwdriver. Adjusting the setting, he aimed it at one of the roundels. There was a sharp click and the roundel popped out of the wall. He removed it and placed it on the floor and in its place was a dark hole with a single outlet and below that, a console with several buttons.

"I see," the Doctor muttered. "This isn't good."

"What is it?" Sarah came to stand beside him.

"He wants me to invert the psychic dampening field. The cord is hooked up to the auxiliary internal shielding circuit. If I do this, the fields will be reversed. Rather than being contained within the Zero Room, the psychic dampening field will expand to the entire interior of the TARDIS, leaving this room at its center without any protection."

Sarah tried to keep up with what he was saying, but in the end just decided to go along with it. Except… "He?" she asked.

The Doctor glanced at his palm again. "I think it's me." He plugged the cord into the wall and the light flickered and then the sounds, the energy of the TARDIS, it all came rushing back. The Doctor, ignoring this, turned to face into the room and suddenly everything made sense.

* * *

 _The TARDIS, Earth 2007 A.D._

The Doctor found himself again in the corridor. He strode with purpose this time. There was something in his TARDIS and he was going to make sure it didn't gain control. He could sense a psychic current flowing through the halls, feel the slightest touch against his mind. There was one place he could go to think and to plan his move, to get answers.

He rounded the corner and reached out a hand to the door of the Zero Room. A sudden wave of dizziness struck him and he stumbled. Something clattered to the floor at his feet.

On the door was the number seventy-two.

Trying to shake off the disorientation, the Doctor brought his hand up to his forehead. And stopped cold. His fingers were stained with black ink.

As the realization dawned, he slowly turned around.

* * *

 _The TARDIS, lost in transit_

"So it's you," the Doctor said and he was careful not to look away.

The creature was at least six feet tall and its skin was gray. Its face, wrinkled, had eyes set into deep sockets and no discernable mouth. It clicked and chattered like some sort of alien insect and wore a black suit for a reason the Doctor couldn't fathom.

"Doctor, what is it?" Sarah asked, turning her head to look at him.

"Keep your eyes on it," the Doctor said. "I don't know what it's called, only that I've seen its kind before."

"Back in the corridor, I thought I saw…no, but how come I couldn't remember before?"

The alien seemed to analyze them, cocking its head and studying them with those dark eyes.

"I had a feeling you'd be back," the Doctor said. "When I first saw you, I took the liberty of scheduling a meeting." He waved his hand, palm outward where a message was still scribbled upon it. "The Zero Room, the one place you wouldn't be able to penetrate. All I had to do was reverse the fields and make it so this was the only place you could be. Now…what do you want?"

The alien hissed and crackled. And spoke. "The Silence will not fall. Darkness consume you, Doctor, lest the question be answered."

"What question?"

"Trenzalore will burn and you will not be there to fall with it." The Silence paused, its eyes boring into the Doctor. "He will knock four times but you will not save him."

The Doctor's mouth was set in a firm line and when Sarah allowed herself to glance at him out of the corner of her eye, she was shocked by what she saw there. For just a moment, it was like the Doctor was not the Doctor at all.

"Save who?"

The creature didn't answer. Instead, it reached out a finger to point at the Doctor. "There is darkness in you and it is the one thing you cannot run from."

Sparks began to jump across the alien's skin, bright flashes of blue. Sarah gasped and instinctively looked to the Doctor. His first instinct was to protect his companion, this version of a girl he hadn't seen in so long. But when he went to protect her, he stopped.

What was he trying to protect her from?

* * *

 _The TARDIS, Earth 2007 A.D._

The Doctor stood with his back to the door, staring at the creature and somehow he remembered seeing it before. Many times before as he ran through the corridors. Lying on the floor at his feet was a pen. His mind worked rapidly, putting it all together. Somehow this creature had managed to get inside the TARDIS without him knowing, had managed to conceal its very existence from him even after multiple sightings.

"The darkness festers in you," the creature said, its voice chilling. "Yet there is something else that would conceal it."

Something wasn't quite right. The Doctor thought back to when he'd been about to destroy the Daleks and had woken up here, in this TARDIS he recognized and yet didn't. The piles of clothes he'd found on the floor, many he recognized from previous incarnations, but most he did not. And deeper still, in some part of his mind, he recognized the creature, as if his eyes – not these, but younger eyes, eyes he remembered well – had seen it a long time ago and had forgotten. Images flashed through his mind of being in this same spot. Of running to the Zero Room with Sarah Jane and meeting one of the creatures there.

And yet…

"I know I haven't seen you before," the Doctor said. "And yet it feels like I have." He ran a hand over his hair, muscle memory left over from the previous inhabitant. "The psychological transference," he muttered. The creature continued to stare at him. "I'm a bloody idiot for not seeing it sooner. At least not admitting it to myself. I really have switched places with him…" A smile spread across his face, the idea was so absurd. "With me."

He reached down and picked up the pen, careful to keep the alien in sight. "So this is my future, is it? Not so bad, I suppose. Except you. I'm afraid you're really going to have to go."

The alien stood still for a moment, making those noises. "You are a fool, Doctor. We have already planted the seed of your own destruction in your mind. That seed will grow and you cannot stop it."

"About that? Yeah, I can feel it. This mind is currently resting, the consciousness elsewhere. But I can feel that darkness. But you're not the only one with tricks." The Doctor put one hand on his head and winced as if with a sudden pain. "See, I'm not the person you expected to find. I'm the younger, happier version. The one you're looking for is the moody one who's been shouldering that darkness all this time. But I have a feeling he's dealing with that even now.

"Something happened, I don't know what, but I'm going to put my faith in it. Something switched our consciousnesses and it had to be for a reason." Without turning, he opened the door to the Zero Room. The alien stepped closer, agitated.

"We should have killed you."

"Yeah, well, your mistake." Before the alien could say anything further or attack, the Doctor threw himself into the Zero Room and slammed the door, at the same time concentrating on that seed of darkness he felt in his mind, trying to tug it free.

"The least I could do is take care of this for you," he murmured and slumped to the ground.

* * *

 _Somewhere in another dimension_

The agitation left the time stream and it began to flow smoothly once again.

With a last relieved chime, the cloister bell fell silent.

* * *

 _Skaro, 1500 A.D._

"Doctor?"

He started at the voice, looked down at the wires in his hand. The destruction of the Daleks, saving all those countless lives, it was so easy. And yet –

"This isn't right," the Doctor said. "Who am I to do this? No one should have such power." He threw down the wires. The Dalek race would not die this day.

"Doctor…?"

Deep in his mind, he felt a darkness settling in. One day in his future, he knew it would greatly dictate his actions. But not today.

Turning away from the horrifying choice he'd been given, the Doctor walked on and his companions followed.

* * *

 _Earth, 2007 A.D._

"Doctor, you can stop now," said a voice from above him and the Doctor snapped out of his thoughts. Before him, the empress burned but for some reason he couldn't remember, his mind felt light. It was as if some heavy burden had been lifted from his shoulders and he looked up from under wet bangs to find Donna standing on the balcony, waiting for him.

Amidst the fire and the rain, the Doctor heeded his companion's call and lived.

* * *

 _Demons Run, 5159 A.D._

Madame Kovarian stared out the porthole into the stars and the airless rock, thinking about what the Silence had told her. She clenched her fists until her nails bit deep into the flesh, drawing beads of blood.

"So even after all that trouble, the prophecy will still come to pass," she spat. It had been such a clever plan. Plant the seed of darkness within the Doctor's mind, watch him wither from within until the darkness consumed him, until his veins ran cold. He would have valued his own life far above anyone else's and would have left that foolish human to die instead of sacrificing himself.

Now her patience was running thin. She wanted him dead.

"But that psychological transference…" she muttered. It was no coincidence. No way some random phenomenon had caused two of his incarnations to switch minds, thus defeating her plan. The Plethora. Damn! It had to be them. If anything ever wanted to get in her way and ensure her failure, even if it meant the Doctor's continued existence, it just _had_ to be them.

Kovarian slammed her fist onto the table. She looked up at the temporal displays and suddenly the tension left her.

"You. Over here." She snapped her fingers at one of the soldiers and pointed at the screen. "This girl here. She will travel with the Doctor." The man she'd summoned didn't speak, only stared at the screen. It depicted a young red-haired woman. Only it wasn't the woman who so caught her interest, rather the child she was so obviously expecting.

A child so obliviously hurtling through time before it could so much as take its first breath.

Madame Kovarian smiled wickedly. Perhaps there was yet a way to salvage this mess. After all, nothing said the Doctor's death had to be by her own hands.

 **END**


End file.
